Other attempts to distribute light over the years have used fiber optics, quartz rods, tubes, diffusers and various light guides. Usually differences in refractive index contain or controllably allow the light to emerge. In all these attempts actual light distribution performance is poor and the structures unwieldly and costly.
Other techniques have used fluorescent and neon filled tubes, or films in tubular structures, which are expensive and need high voltages. Also these tubes cannot be cut or extended easily, and it is difficult to provide continuous uninterrupted light or have broad light spectra with these tubes.
In particular, an earlier attempt is found in U.S. Pat. No. 4,460,940 entitled "Apparatus for uniform illumination employing light diffuser" by Kei Mori. Mori uses non-collimated light, which enters a transmitting element, a portion is conducted to the diffusing element having a different refractive index from the transmitting element, and emerges. The combination provides that only a given wavelength emerge from the device at a particular exit. The intensity of this single wavelength emerging light at any particular exit may be uniform over the particular exit, but it will not be the same intensity as other wavelengths at other exits. This is due to the fact that the light source has differing intensity levels at differing wavelengths. In addition there is less light available as the particular exit is further away from the light source.
It is also clear that when single or few wavelength are emitted the resulting emerging light will be dim and useful for very small indicators in dark areas.
Another attempt is shown in U.S. Pat. No. 4,422,719 entitled "Optical distribution system including light guide" to Orcutt. Here noncollimated light enters a transmitting element. There is a transparent or translucent sleeve around the transmitting element having a different refractive index from the transmitting element. There will be light emerging along the entire sleeve but the intensity will decrease as the distance from the light source increases. The emitted light will not be of a uniform intensity along the optical path of the transmitting element.
In both of the Mori and the Orcutt patents the light is less intense as the distance from the source increases, hence the light emerging along the optical path is less intense than that closer to the light source. This occurs since less and less light is available as the distance increases because some has already emerged out from the apparatus. There is no mechanism to distribute the entering light proportionally along the optical path length of the system.
It is an object of this invention to overcome the limitations of the aforementioned inventions and produce an apparatus which produces uniform light intensity over the entire emitting surface.
It is another object of this invention to provide a means to mix and blend colors within the light guides of this invention.